This invention relates to a matching circuit arrangement for operating a high-pressure discharge lamp. This circuit arrangement is provided with two input terminals for connection to a supply source, each of these input terminals being connected to a respective output terminal, which output terminals are intended to connect the high-pressure discharge lamp. A controlled semiconductor switching element A having a thyristor characteristic is included in at least one connection between an input terminal and the respective output terminal in such a manner that a main electrode AE1 of the switching element A is electrically connected to the output terminal and a main electrode AE2 is connected to the input terminal, while switching element A is provided with a control electrode AS, whose control signal depends upon the voltage variation across a voltage divider circuit coupled between the two input terminals. The invention further relates to a lamp provided with such a matching circuit arrangement.
A circuit arrangement of the kind mentioned in the preceding paragraph is known from U.S. Pat. No. 4,342,948. Such a matching circuit permits a high-pressure discharge lamp to be operated in an apparatus which is provided with a stabilization ballast not adapted to the relevant lamp. Besides an increasing improvement with respect to luminous efficacy of high-pressure discharge lamps, while maintaining a desired illumination intensity, inter alia a saving of energy can thus be obtained in an existing apparatus.
In the known circuit arrangement, the control signal flows in the switching element A between the control electrode AS and the main electrode AE2, which is connected to the input terminal of the matching circuit. Controlled semiconductor switching elements having a thyristor characteristic are in practice constructed so that the metallic envelope is electrically shortcircuited with a main electrode, i.e. that main electrode across which no control signal is passed.
For the known circuit arrangement, this means that the relevant output terminal is electrically connected to the metallic envelope of the switching element A. When the matching circuit is incorporated in an equipment, for example, in a lamp base, this leads to the metallic envelope of switching element A being electrically insulated from the external input terminals for connection to a supply source present at the equipment, in this case the lamp base. As far as measures are required for cooling switching element A during operation, this has proved to be disadvantageous.